(1) Field of the Invention
The present invention generally relates to a fixture used for testing the bond strength of a coating affixed to the surface of a body. More particularly the fixture holds the body, that is cylindrical in shape, in an optimal position, throughout a process of peeling the affixed coating off. When used in conjunction with proper state-of-the-art instrumentation the inventive fixture provides a means for evaluating the peel strength of the adhesive bond between the coating and the cylindrical body. The inventive device is particularly suitable for use in measuring the peel strength of elastomeric coatings bonded to the outside of steel cylinders; the initial application being transducer bodies.
(2) Description of the Prior Art
The present invention relates to the measurement of the bonding of elastomers to the outside of different transducer bodies. All of the bodies are steel cylinders. It was found not to be conducive to test other geometric shapes as the condition of the materials, and the techniques used to apply the elastomer and adhesive, and the curing cycles all would be different. The resulting information would be different and not as valuable.
Other types of peel tests include flat plate tests. The angle of peel (90.degree.) for a steel cylinder is essentially the same as that of a flat plate test. However, the details learned in applying the adhesive and rubbers to a steel cylinder which is the actual shape of the components to be used yields superior practical data.
There are two prior art variations of the flat plate 90.degree. peel test. One uses a sliding plate fixture that holds a flat plate secure in a set of clamps. The fixture and sample are perpendicular to the angle of pull. The fact that the plate slides, maintains a constant angle relative to the pulling direction. The other test uses a flat plate that has one end bent into the shape of an L. Onto the surface of this plate is bonded the test material. The bent leg of the plate is gripped in a clamping fixture and held stationary. A flap of the elastomer is clasped in another grip and pulled away from the plate. A major disadvantage here is that the angle of pull is not constant and thereby provides semi-false information.
Also, in conjunction with peel tests for cylindrical bodies, dimensional accuracy is very critical. If the fixturing is inaccurate, the values will be in error. If the sample is skewed or twisted, the angle of pull will not be perpendicular to the test sample, and the bond-line will be twisted as well. Instead of the force acting on the bond-line straight across the width of the test sample (the shortest distance), it will act across a longer bond-line. This longer line of action will take a larger, erroneous force. It is also possible for the resulting mode of adhesive failure to be different.